path: root/sys/net/if_tap.c

/*
 * Copyright (C) 1999-2000 by Maksim Yevmenkin <m_evmenkin@yahoo.com>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * BASED ON:
 * -------------------------------------------------------------------------
 *
 * Copyright (c) 1988, Julian Onions <jpo@cs.nott.ac.uk>
 * Nottingham University 1987.
 */

/*
 * $FreeBSD$
 * $Id: if_tap.c,v 0.21 2000/07/23 21:46:02 max Exp $
 */

#include "opt_inet.h"

#include <sys/param.h>
#include <sys/conf.h>
#include <sys/filedesc.h>
#include <sys/filio.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/poll.h>
#include <sys/proc.h>
#include <sys/signalvar.h>
#include <sys/socket.h>
#include <sys/sockio.h>
#include <sys/sysctl.h>
#include <sys/systm.h>
#include <sys/ttycom.h>
#include <sys/uio.h>
#include <sys/vnode.h>

#include <net/bpf.h>
#include <net/ethernet.h>
#include <net/if.h>
#include <net/if_arp.h>
#include <net/route.h>

#include <netinet/in.h>

#include <net/if_tapvar.h>
#include <net/if_tap.h>


#define CDEV_NAME	"tap"
#define CDEV_MAJOR	149
#define TAPDEBUG	if (tapdebug) printf

#define TAP		"tap"
#define VMNET		"vmnet"
#define VMNET_DEV_MASK	0x00010000

/* module */
static int 		tapmodevent	__P((module_t, int, void *));

/* device */
static void		tapclone	__P((void *, char *, int, dev_t *));
static void		tapcreate	__P((dev_t));

/* network interface */
static void		tapifstart	__P((struct ifnet *));
static int		tapifioctl	__P((struct ifnet *, u_long, caddr_t));
static void		tapifinit	__P((void *));

/* character device */
static d_open_t		tapopen;
static d_close_t	tapclose;
static d_read_t		tapread;
static d_write_t	tapwrite;
static d_ioctl_t	tapioctl;
static d_poll_t		tappoll;

static struct cdevsw	tap_cdevsw = {
	/* open */	tapopen,
	/* close */	tapclose,
	/* read */	tapread,
	/* write */	tapwrite,
	/* ioctl */	tapioctl,
	/* poll */	tappoll,
	/* mmap */	nommap,
	/* startegy */	nostrategy,
	/* dev name */	CDEV_NAME,
	/* dev major */	CDEV_MAJOR,
	/* dump */	nodump,
	/* psize */	nopsize,
	/* flags */	0,
};

static int		taprefcnt = 0;		/* module ref. counter   */
static int		taplastunit = -1;	/* max. open unit number */
static int		tapdebug = 0;		/* debug flag            */

MALLOC_DECLARE(M_TAP);
MALLOC_DEFINE(M_TAP, CDEV_NAME, "Ethernet tunnel interface");
SYSCTL_INT(_debug, OID_AUTO, if_tap_debug, CTLFLAG_RW, &tapdebug, 0, "");
DEV_MODULE(if_tap, tapmodevent, NULL);

/*
 * tapmodevent
 *
 * module event handler
 */
static int
tapmodevent(mod, type, data)
	module_t	 mod;
	int		 type;
	void		*data;
{
	static int		attached = 0;
	static eventhandler_tag	eh_tag = NULL;

	switch (type) {
	case MOD_LOAD:
		if (attached)
			return (EEXIST);

		eh_tag = EVENTHANDLER_REGISTER(dev_clone, tapclone, 0, 1000);
		cdevsw_add(&tap_cdevsw);
		attached = 1;
	break;

	case MOD_UNLOAD: {
		int	unit;

		if (taprefcnt > 0)
			return (EBUSY);

		EVENTHANDLER_DEREGISTER(dev_clone, eh_tag);
		cdevsw_remove(&tap_cdevsw);

		unit = 0;
		while (unit <= taplastunit) {
			int		 s;
			struct ifnet	*ifp = NULL;

			s = splimp();
			TAILQ_FOREACH(ifp, &ifnet, if_link)
				if ((strcmp(ifp->if_name, TAP) == 0) ||
				    (strcmp(ifp->if_name, VMNET) == 0))
					if (ifp->if_unit == unit)
						break;
			splx(s);

			if (ifp != NULL) {
				struct tap_softc	*tp = ifp->if_softc;

				TAPDEBUG("detaching %s%d. minor = %#x, " \
					"taplastunit = %d\n",
					ifp->if_name, unit, minor(tp->tap_dev),
					taplastunit);

				s = splimp();
				ether_ifdetach(ifp, 1);
				splx(s);
				destroy_dev(tp->tap_dev);
				FREE(tp, M_TAP);
			}
			else
				unit ++;
		}

		attached = 0;
	} break;

	default:
		return (EOPNOTSUPP);
	}

	return (0);
} /* tapmodevent */


/*
 * DEVFS handler
 *
 * We need to support two kind of devices - tap and vmnet
 */
static void
tapclone(arg, name, namelen, dev)
	void	*arg;
	char	*name;
	int	 namelen;
	dev_t	*dev;
{
	int	 unit, minor;
	char	*device_name = NULL;

	if (*dev != NODEV)
		return;

	device_name = TAP;
	if (dev_stdclone(name, NULL, device_name, &unit) != 1) {
		device_name = VMNET;

		if (dev_stdclone(name, NULL, device_name, &unit) != 1)
			return;

		minor = unit2minor(unit |  VMNET_DEV_MASK);
	}
	else
		minor = unit2minor(unit);

	*dev = make_dev(&tap_cdevsw, minor, UID_ROOT, GID_WHEEL, 0600, "%s%d",
			device_name, unit);
} /* tapclone */


/*
 * tapcreate
 *
 * to create interface
 */
static void
tapcreate(dev)
	dev_t	dev;
{
	struct ifnet		*ifp = NULL;
	struct tap_softc	*tp = NULL;
	unsigned short		 macaddr_hi;
	int			 unit, s;
	char			*name = NULL;

	/* allocate driver storage and create device */
	MALLOC(tp, struct tap_softc *, sizeof(*tp), M_TAP, M_WAITOK | M_ZERO);

	/* select device: tap or vmnet */
	if (minor(dev) & VMNET_DEV_MASK) {
		name = VMNET;
		unit = dev2unit(dev) & 0xff;
		tp->tap_flags |= TAP_VMNET;
	}
	else {
		name = TAP;
		unit = dev2unit(dev);
	}

	tp->tap_dev = make_dev(&tap_cdevsw, minor(dev), UID_ROOT, GID_WHEEL, 
						0600, "%s%d", name, unit);
	tp->tap_dev->si_drv1 = dev->si_drv1 = tp;

	/* generate fake MAC address: 00 bd xx xx xx unit_no */
	macaddr_hi = htons(0x00bd);
	bcopy(&macaddr_hi, &tp->arpcom.ac_enaddr[0], sizeof(short));
	bcopy(&ticks, &tp->arpcom.ac_enaddr[2], sizeof(long));
	tp->arpcom.ac_enaddr[5] = (u_char)unit;

	/* fill the rest and attach interface */	
	ifp = &tp->tap_if;
	ifp->if_softc = tp;

	ifp->if_unit = unit;
	if (unit > taplastunit)
		taplastunit = unit;

	ifp->if_name = name;
	ifp->if_init = tapifinit;
	ifp->if_output = ether_output;
	ifp->if_start = tapifstart;
	ifp->if_ioctl = tapifioctl;
	ifp->if_mtu = ETHERMTU;
	ifp->if_flags = (IFF_BROADCAST|IFF_SIMPLEX|IFF_MULTICAST);
	ifp->if_snd.ifq_maxlen = ifqmaxlen;

	s = splimp();
	ether_ifattach(ifp, 1);
	splx(s);

	tp->tap_flags |= TAP_INITED;

	TAPDEBUG("interface %s%d created. minor = %#x\n",
			ifp->if_name, ifp->if_unit, minor(tp->tap_dev));
} /* tapcreate */


/*
 * tapopen 
 *
 * to open tunnel. must be superuser
 */
static int
tapopen(dev, flag, mode, p)
	dev_t		 dev;
	int		 flag;
	int		 mode;
	struct proc	*p;
{
	struct tap_softc	*tp = NULL;
	int			 error;

	if ((error = suser(p)) != 0)
		return (error);

	tp = dev->si_drv1;
	if (tp == NULL) {
		tapcreate(dev);
		tp = dev->si_drv1;
	}

	if (tp->tap_flags & TAP_OPEN)
		return (EBUSY);

	bcopy(tp->arpcom.ac_enaddr, tp->ether_addr, sizeof(tp->ether_addr));

	tp->tap_pid = p->p_pid;
	tp->tap_flags |= TAP_OPEN;
	taprefcnt ++;

	TAPDEBUG("%s%d is open. minor = %#x, refcnt = %d, taplastunit = %d\n",
		tp->tap_if.if_name, tp->tap_if.if_unit,
		minor(tp->tap_dev), taprefcnt, taplastunit);

	return (0);
} /* tapopen */


/*
 * tapclose
 *
 * close the device - mark i/f down & delete routing info
 */
static int
tapclose(dev, foo, bar, p)
	dev_t		 dev;
	int		 foo;
	int		 bar;
	struct proc	*p;
{
	int			 s;
	struct tap_softc	*tp = dev->si_drv1;
	struct ifnet		*ifp = &tp->tap_if;
	struct mbuf		*m = NULL;

	/* junk all pending output */

	s = splimp();
	do {
		IF_DEQUEUE(&ifp->if_snd, m);
		if (m != NULL)
			m_freem(m);
	} while (m != NULL);
	splx(s);

	/*
	 * do not bring the interface down, and do not anything with
	 * interface, if we are in VMnet mode. just close the device.
	 */

	if (((tp->tap_flags & TAP_VMNET) == 0) && (ifp->if_flags & IFF_UP)) {
		s = splimp();
		if_down(ifp);
		if (ifp->if_flags & IFF_RUNNING) {
			/* find internet addresses and delete routes */
			struct ifaddr	*ifa = NULL;

			TAILQ_FOREACH(ifa, &ifp->if_addrhead, ifa_link) {
				if (ifa->ifa_addr->sa_family == AF_INET) {
					rtinit(ifa, (int)RTM_DELETE, 0);

					/* remove address from interface */
					bzero(ifa->ifa_addr, 
						   sizeof(*(ifa->ifa_addr)));
					bzero(ifa->ifa_dstaddr, 
						   sizeof(*(ifa->ifa_dstaddr)));
					bzero(ifa->ifa_netmask, 
						   sizeof(*(ifa->ifa_netmask)));
				}
			}

			ifp->if_flags &= ~IFF_RUNNING;
		}
		splx(s);
	}

	funsetown(tp->tap_sigio);
	selwakeup(&tp->tap_rsel);

	tp->tap_flags &= ~TAP_OPEN;
	tp->tap_pid = 0;

	taprefcnt --;
	if (taprefcnt < 0) {
		taprefcnt = 0;
		printf("%s%d minor = %#x, refcnt = %d is out of sync. " \
			"set refcnt to 0\n", ifp->if_name, ifp->if_unit, 
			minor(tp->tap_dev), taprefcnt);
	}

	TAPDEBUG("%s%d is closed. minor = %#x, refcnt = %d, taplastunit = %d\n",
			ifp->if_name, ifp->if_unit, minor(tp->tap_dev),
			taprefcnt, taplastunit);

	return (0);
} /* tapclose */


/*
 * tapifinit
 *
 * network interface initialization function
 */
static void
tapifinit(xtp)
	void	*xtp;
{
	struct tap_softc	*tp = (struct tap_softc *)xtp;
	struct ifnet		*ifp = &tp->tap_if;

	TAPDEBUG("initializing %s%d, minor = %#x\n",
			ifp->if_name, ifp->if_unit, minor(tp->tap_dev));

	ifp->if_flags |= IFF_RUNNING;
	ifp->if_flags &= ~IFF_OACTIVE;

	/* attempt to start output */
	tapifstart(ifp);
} /* tapifinit */


/*
 * tapifioctl
 *
 * Process an ioctl request on network interface
 */
int
tapifioctl(ifp, cmd, data)
	struct ifnet	*ifp;
	u_long		 cmd;
	caddr_t		 data;
{
	struct tap_softc 	*tp = (struct tap_softc *)(ifp->if_softc);
	struct ifstat		*ifs = NULL;
	int			 s, dummy;

	switch (cmd) {
		case SIOCSIFADDR:
		case SIOCGIFADDR:
		case SIOCSIFMTU:
			s = splimp();
			dummy = ether_ioctl(ifp, cmd, data);
			splx(s);
			return (dummy);

		case SIOCSIFFLAGS: /* XXX -- just like vmnet does */
		case SIOCADDMULTI:
		case SIOCDELMULTI:
		break;

		case SIOCGIFSTATUS:
			s = splimp();
			ifs = (struct ifstat *)data;
			dummy = strlen(ifs->ascii);
			if (tp->tap_pid != 0 && dummy < sizeof(ifs->ascii))
				snprintf(ifs->ascii + dummy,
					sizeof(ifs->ascii) - dummy,
					"\tOpened by PID %d\n", tp->tap_pid);
			splx(s);
		break;

		default:
			return (EINVAL);
	}

	return (0);
} /* tapifioctl */


/*
 * tapifstart 
 * 
 * queue packets from higher level ready to put out
 */
static void
tapifstart(ifp)
	struct ifnet	*ifp;
{
	struct tap_softc	*tp = ifp->if_softc;
	int			 s;

	TAPDEBUG("%s%d starting, minor = %#x\n", 
			ifp->if_name, ifp->if_unit, minor(tp->tap_dev));

	/*
	 * do not junk pending output if we are in VMnet mode.
	 * XXX: can this do any harm because of queue overflow?
	 */

	if (((tp->tap_flags & TAP_VMNET) == 0) && 
	    ((tp->tap_flags & TAP_READY) != TAP_READY)) {
		struct mbuf	*m = NULL;

		TAPDEBUG("%s%d not ready. minor = %#x, tap_flags = 0x%x\n",
			ifp->if_name, ifp->if_unit,
			minor(tp->tap_dev), tp->tap_flags);

		s = splimp();
		do {
			IF_DEQUEUE(&ifp->if_snd, m);
			if (m != NULL)
				m_freem(m);
			ifp->if_oerrors ++;
		} while (m != NULL);
		splx(s);

		return;
	}

	s = splimp();
	ifp->if_flags |= IFF_OACTIVE;

	if (ifp->if_snd.ifq_len != 0) {
		if (tp->tap_flags & TAP_RWAIT) {
			tp->tap_flags &= ~TAP_RWAIT;
			wakeup((caddr_t)tp);
		}

		if ((tp->tap_flags & TAP_ASYNC) && (tp->tap_sigio != NULL))
			pgsigio(tp->tap_sigio, SIGIO, 0);

		selwakeup(&tp->tap_rsel);
		ifp->if_opackets ++; /* obytes are counted in ether_output */
	}

	ifp->if_flags &= ~IFF_OACTIVE;
	splx(s);
} /* tapifstart */


/*
 * tapioctl
 *
 * the cdevsw interface is now pretty minimal
 */
static int
tapioctl(dev, cmd, data, flag, p)
	dev_t		 dev;
	u_long		 cmd;
	caddr_t		 data;
	int		 flag;
	struct proc	*p;
{
	struct tap_softc	*tp = dev->si_drv1;
	struct ifnet		*ifp = &tp->tap_if;
 	struct tapinfo		*tapp = NULL;
	int			 s;

	switch (cmd) {
 		case TAPSIFINFO:
			s = splimp();
 		        tapp = (struct tapinfo *)data;
 			ifp->if_mtu = tapp->mtu;
 			ifp->if_type = tapp->type;
 			ifp->if_baudrate = tapp->baudrate;
			splx(s);
 		break;

	 	case TAPGIFINFO:
 			tapp = (struct tapinfo *)data;
 			tapp->mtu = ifp->if_mtu;
 			tapp->type = ifp->if_type;
 			tapp->baudrate = ifp->if_baudrate;
 		break;

		case TAPSDEBUG:
			tapdebug = *(int *)data;
		break;

		case TAPGDEBUG:
			*(int *)data = tapdebug;
		break;

		case FIONBIO:
		break;

		case FIOASYNC:
			s = splimp();
			if (*(int *)data)
				tp->tap_flags |= TAP_ASYNC;
			else
				tp->tap_flags &= ~TAP_ASYNC;
			splx(s);
		break;

		case FIONREAD:
			s = splimp();
			if (ifp->if_snd.ifq_head) {
				struct mbuf	*mb = ifp->if_snd.ifq_head;

				for(*(int *)data = 0;mb != NULL;mb = mb->m_next)
					*(int *)data += mb->m_len;
			} 
			else
				*(int *)data = 0;
			splx(s);
		break;

		case FIOSETOWN:
			return (fsetown(*(int *)data, &tp->tap_sigio));

		case FIOGETOWN:
			*(int *)data = fgetown(tp->tap_sigio);
			return (0);

		/* this is deprecated, FIOSETOWN should be used instead */
		case TIOCSPGRP:
			return (fsetown(-(*(int *)data), &tp->tap_sigio));

		/* this is deprecated, FIOGETOWN should be used instead */
		case TIOCGPGRP:
			*(int *)data = -fgetown(tp->tap_sigio);
			return (0);

		/* VMware/VMnet port ioctl's */

		case SIOCGIFFLAGS:	/* get ifnet flags */
			bcopy(&ifp->if_flags, data, sizeof(ifp->if_flags));
		break;

		case VMIO_SIOCSIFFLAGS: { /* VMware/VMnet SIOCSIFFLAGS */
			short	f = *(short *)data;

			f &= 0x0fff;
			f &= ~IFF_CANTCHANGE;
			f |= IFF_UP;

			s = splimp();
			ifp->if_flags = f | (ifp->if_flags & IFF_CANTCHANGE);
			splx(s);
		} break;

		case OSIOCGIFADDR:	/* get MAC address of the remote side */
		case SIOCGIFADDR:
			bcopy(tp->ether_addr, data, sizeof(tp->ether_addr));
		break;

		case SIOCSIFADDR:	/* set MAC address of the remote side */
			bcopy(data, tp->ether_addr, sizeof(tp->ether_addr));
		break;

		default:
			return (ENOTTY);
	}
	return (0);
} /* tapioctl */


/*
 * tapread
 *
 * the cdevsw read interface - reads a packet at a time, or at
 * least as much of a packet as can be read
 */
static int
tapread(dev, uio, flag)
	dev_t		 dev;
	struct uio	*uio;
	int		 flag;
{
	struct tap_softc	*tp = dev->si_drv1;
	struct ifnet		*ifp = &tp->tap_if;
	struct mbuf		*m = NULL, *m0 = NULL;
	int			 error = 0, len, s;

	TAPDEBUG("%s%d reading, minor = %#x\n",
			ifp->if_name, ifp->if_unit, minor(tp->tap_dev));

	if ((tp->tap_flags & TAP_READY) != TAP_READY) {
		TAPDEBUG("%s%d not ready. minor = %#x, tap_flags = 0x%x\n",
				ifp->if_name, ifp->if_unit, 
				minor(tp->tap_dev), tp->tap_flags);

		return (EHOSTDOWN);
	}

	tp->tap_flags &= ~TAP_RWAIT;

	/* sleep until we get a packet */
	do {
		s = splimp();
		IF_DEQUEUE(&ifp->if_snd, m0);
		splx(s);

		if (m0 == NULL) {
			if (flag & IO_NDELAY)
				return (EWOULDBLOCK);
			
			tp->tap_flags |= TAP_RWAIT;
			error = tsleep((caddr_t)tp,PCATCH|(PZERO+1),"taprd",0);
			if (error)
				return (error);
		}
	} while (m0 == NULL);

	/* feed packet to bpf */
	if (ifp->if_bpf != NULL)
		bpf_mtap(ifp, m0);

	/* xfer packet to user space */
	while ((m0 != NULL) && (uio->uio_resid > 0) && (error == 0)) {
		len = min(uio->uio_resid, m0->m_len);
		if (len == 0)
			break;

		error = uiomove(mtod(m0, caddr_t), len, uio);
		MFREE(m0, m);
		m0 = m;
	}

	if (m0 != NULL) {
		TAPDEBUG("%s%d dropping mbuf, minor = %#x\n",
				ifp->if_name, ifp->if_unit, minor(tp->tap_dev));
		m_freem(m0);
	}

	return (error);
} /* tapread */


/*
 * tapwrite
 *
 * the cdevsw write interface - an atomic write is a packet - or else!
 */
static int
tapwrite(dev, uio, flag)
	dev_t		 dev;
	struct uio	*uio;
	int		 flag;
{
	struct tap_softc	*tp = dev->si_drv1;
	struct ifnet		*ifp = &tp->tap_if;
	struct mbuf		*top = NULL, **mp = NULL, *m = NULL;
	struct ether_header	*eh = NULL;
	int		 	 error = 0, tlen, mlen;

	TAPDEBUG("%s%d writting, minor = %#x\n",
				ifp->if_name, ifp->if_unit, minor(tp->tap_dev));

	if (uio->uio_resid == 0)
		return (0);

	if ((uio->uio_resid < 0) || (uio->uio_resid > TAPMRU)) {
		TAPDEBUG("%s%d invalid packet len = %d, minor = %#x\n",
				ifp->if_name, ifp->if_unit, 
				uio->uio_resid, minor(tp->tap_dev));

		return (EIO);
	}
	tlen = uio->uio_resid;

	/* get a header mbuf */
	MGETHDR(m, M_DONTWAIT, MT_DATA);
	if (m == NULL)
		return (ENOBUFS);
	mlen = MHLEN;

	top = 0;
	mp = &top;
	while ((error == 0) && (uio->uio_resid > 0)) {
		m->m_len = min(mlen, uio->uio_resid);
		error = uiomove(mtod(m, caddr_t), m->m_len, uio);
		*mp = m;
		mp = &m->m_next;
		if (uio->uio_resid > 0) {
			MGET(m, M_DONTWAIT, MT_DATA);
			if (m == NULL) {
				error = ENOBUFS;
				break;
			}
			mlen = MLEN;
		}
	}
	if (error) {
		ifp->if_ierrors ++;
		if (top)
			m_freem(top);
		return (error);
	}

	top->m_pkthdr.len = tlen;
	top->m_pkthdr.rcvif = ifp;
	
	/*
	 * Ethernet bridge and bpf are handled in ether_input
	 *
	 * adjust mbuf and give packet to the ether_input
	 */

	eh = mtod(top, struct ether_header *);
	m_adj(top, sizeof(struct ether_header));
	ether_input(ifp, eh, top);
	ifp->if_ipackets ++; /* ibytes are counted in ether_input */

	return (0);
} /* tapwrite */


/*
 * tappoll
 *
 * the poll interface, this is only useful on reads
 * really. the write detect always returns true, write never blocks
 * anyway, it either accepts the packet or drops it
 */
static int
tappoll(dev, events, p)
	dev_t		 dev;
	int		 events;
	struct proc	*p;
{
	struct tap_softc	*tp = dev->si_drv1;
	struct ifnet		*ifp = &tp->tap_if;
	int		 	 s, revents = 0;

	TAPDEBUG("%s%d polling, minor = %#x\n",
				ifp->if_name, ifp->if_unit, minor(tp->tap_dev));

	s = splimp();
	if (events & (POLLIN | POLLRDNORM)) {
		if (ifp->if_snd.ifq_len > 0) {
			TAPDEBUG("%s%d have data in queue. len = %d, " \
				"minor = %#x\n", ifp->if_name, ifp->if_unit,
				ifp->if_snd.ifq_len, minor(tp->tap_dev));

			revents |= (events & (POLLIN | POLLRDNORM));
		} 
		else {
			TAPDEBUG("%s%d waiting for data, minor = %#x\n",
				ifp->if_name, ifp->if_unit, minor(tp->tap_dev));

			selrecord(p, &tp->tap_rsel);
		}
	}

	if (events & (POLLOUT | POLLWRNORM))
		revents |= (events & (POLLOUT | POLLWRNORM));

	splx(s);
	return (revents);
} /* tappoll */